well i just reformatted my gf's dell laptop and win update didnt have it either...so i jsut went to the dell website, entered her service tag code and found it.
Ah I figured out. I did some browsing on HP site and it turns out that I needed UAA (Universal Audio Architecture). Once I installed that, Windows update was able to find the audio driver I needed.
I was going to say to install the nvidia chipset. any nforce chipset would have worked. this would have made the audio driver recognizable. my second option was to for you to see if it was an msi board (hp loves them). you can use auto update at their website